User's Manual Part 1
Release8OverviewofCycloneNetworks
Issue2,November2007 Draft5forRegulatoryReview 99
8 MEETINGLINKREQUIREMENTS
8.1 AP‐SMLINKS
APs communicate with SMs using a point-to-multipoint protocol. An AP-SM link has lower
throughput and higher latency than a backhaul link for two reasons:
• Many endpoints are involved.
• The bandwidth request and reservation process consumes bandwidth.
In the 900-MHz frequency band range, round-trip latency is typically
• 40 msec with software scheduling.
• 15 msec with hardware scheduling.
In all other Cyclone frequency band ranges, round-trip latency is typically
• 15 msec with software scheduling.
• 6 msec with hardware scheduling.
At range settings of greater than 40 miles (64 km) in the 900-MHz AP, more time elapses
between transmit and receive cycles to compensate for greater air delay. In each frame,
this reduces the number of data slots, which slightly reduces the aggregate throughput of
the link. However, the throughput is as predictable as in other Cyclone point-to-multipoint
links.
Throughput is a factor of the Max Range parameter in the AP and is effective for all SMs,
regardless of their distance from the AP. Throughput includes all downlink data to all SMs
and all uplink data from all SMs that link to the AP. For throughput with hardware
scheduling, see
Table 13 on Page 62.
End user perspective of throughput is based on both bandwidth in the sending direction
and the return of TCP acknowledgement packets in the other. Where sufficient downlink
bandwidth exists to support downlink traffic and overhead, transient traffic congestion in
the uplink can cause some TCP acknowledgement packets to be dropped, and the end
user to perceive a reduction in throughput. This can also occur with sufficient uplink
bandwidth and dropping acknowledgment packets in the downlink.
However, a Cyclone network operator can optionally enable the Prioritize TCP ACK
parameter in the AP and BHM, giving these packets priority over other packet types.
This results in fewer of them being dropped.
The effects of changing network conditions on PTMP throughput are indicated in
Table 24.